There's a lot of quackery surrounding this epidemic, so I thought long and hard before writing this. I have been following/researching global studies into vitamin D for nigh on a decade now.... originally it was with a view to making a television programme about it.
Vitamin D ... not a vitamin really ... it's a hormone. We produce it when certain frequencies of UV light hit our skin. If we are light skinned, we produce it more quickly than if we are dark skinned.
The headline news is that it may well have significant protective properties where covid 19 is concerned: it is crucial to the regulation of our immune systems, we have seasonal patterns of deficiency which correlate with corona virus vulnerability, it compromises this particular coronavirus' spike proteins that allow it to bind onto our cells and it helps to regulate our response to the virus. Evidence is growing that groups deficient in vitamin D (the old, diabetics, ethnic groups with dark skin) correlate with the groups most at risk from becoming seriously ill (from a virus that most people will shrug off).
I can link to a basket full of writing in the BMJ and other such reputable sources but, to be honest, it would be a waste of time. You'd be better off spending that time grabbing some high strength codliver oil capsules, vitamin D3 supplements or just exposing some skin to sunshine. It won't harm you and it night just save you from getting very sick.
If I get sick and die, you can disregard this, as I've been dosing on vit D for years.
I read a lot about Vit D a few years back and believe it has great benefits. I took 3-4000 iu per day which is probably at the top end of what you should be taking but is considered a safe amount. I believe it contributed to my kidney stones though, because that amount with the very high protein diet I have for bodybuilding wasn't the best idea. I just stick to sardines or salmon everyday now to get it.
A good way to get it (aside from the best way, which is sunshine) is in codliver oil. I take 1000mg a day (Holland and Barrett's high strength capsules). You get other benefits like Omega acids etc. They currently have an offer on, BOGOF on the large jars. Pretty much a year's supply.
The ethnic grouping point really brought it home yesterday with the mention that all the medical teams that had passed had been of African/asian origin - and the lack of Vitamin D would have been a factor in this.
"Northerly resident; Europeans with darker skins; BAME, and African Americans; as well as more southerly elderly Spanish and Italians; are often vitamin D deficient. IF, vitamin D deficiency, increases the risk of COVID-19 related; infection, hospitalisation and mortality; one would expect, and indeed sees, higher COVID-19 hospitalisation and mortality, in; dark-skinned (Fitzpatrick scale) northerly residents; those with dress codes that inhibit sunlight; and generally in groups likely to include the ‘D’ deficient. "
Im not a fan of cheap cod liver oil tablets. There are better ways of getting your vit D and essential fatty acids without taking rancid cod liver oil tablets. Personally I have plenty sardines and salmon, and top that up with cold pressed flax seed oil.
Too much Vitamin D isn't good for you either though the Mayo clinic implies 4000 IU a day is the upper limit. Way more than most supplements. Vitamin D plays a role both in supporting the immune system response and in reducing respiratory inflammation (from cytokine storm perhaps). One study I ready suggested that low Vitamin D made you 30% more likely to have a respiratory illness, and the symptoms were also worse. There are also government metrics suggesting 25% of adults have low Vitamin D and advising that medical practitioners advise supplementation. Zinc has also shown some interruption of viral reproduction. My doctor recommended supplementing on both. Why take the risk?